Cure behavior of dye-doped epoxy system for 2-photon fluorescence imaging

The development of a novel non-destructive evaluation method using multiphoton imaging techniques has been proposed. In order to implement this technique in structural composites, two-photon-absorbing chromophore dyes must be incorporated into the composite matrix. Optical absorbance studies indicate a fluorescent-active matrix material has been created by physical mixing of DGEBA, DETA and the chromophore Rhodamine B. The effect of chromophore addition and concentration on cure behavior and mechanical properties of DGEBA-DETA has been investigated using dynamic and isothermal differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Dynamic DSC measurements show decreased extent of cure as dye concentrations increase. Isothermal DSC measurements also show that degree of cure decreases with increasing dye concentration, with the effect stronger at higher cure temperatures. Evaluation of cure kinetics using 2^nd-order autocatalytic model does not show any obvious change in activation energy of primary- and secondary-amine epoxy reactions due to dye incorporation; investigations into the etherification reaction and possible catalysis of etherification by the fluorescent dye are suggested. The glass transition temperature of fully-cured systems decreases, approximately linearly, with increasing dye concentration - up to 5% decrease with 1.2wt% dye, which is predicted by decreased degree-of-cure. Flexural modulus of fully-cured systems does not appear to be affected by dye incorporation, and shows no concentration dependence.